Fix some outstanding issues with the pxa2xx_spi driver when running on a
PXA270:

- Wrong timeout calculation in the setup function due to different
  peripheral clock rates in the PXAxxx family.

- Bad handling of SSSR_TFS interrupts in interrupt_transfer function.

- Added locking to interface between the pump_messages workqueue and the
  pump_transfers tasklet.

Much thanks to Juergen Beisert for the extensive testing on the PXA270.
Signed-off-by: Stephen Street <stephen@streetfiresound.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>